refactor(status): Support batch and all changes discard functionality

The file discarding mechanism has been significantly refactored to improve handling of multi-file operations. Instead of processing discards on a per-file basis, the system now supports batch actions for selected files or reverting all tracked modifications simultaneously. This update centralizes complex discard logic into dedicated functions across the component suite.

- Updated state management and types to handle arrays of file changes.
- Added UI elements and handlers for discarding all staged/unstaged changes.
- Enhanced the confirmation dialog to display multiple discarded targets in a list view.

src/lib/components/StatusPanel.svelte

@@ -15,7 +15,8 @@
     onSelectFile: (file: GitFileStatus) => void;
     onStage: (files: GitFileStatus[]) => void;
     onUnstage: (files: GitFileStatus[]) => void;
-    onDiscard: (file: GitFileStatus, staged: boolean) => void;
+    onDiscard: (files: GitFileStatus[], staged: boolean) => void;
+    onDiscardMany: (files: GitFileStatus[]) => void;
     onPatch: (file: GitFileStatus, staged: boolean) => void;
     onStageAll: () => void;
     onUnstageAll: () => void;
@@ -34,6 +35,7 @@
     onStage = () => {},
     onUnstage = () => {},
     onDiscard = () => {},
+    onDiscardMany = () => {},
     onPatch = () => {},
     onStageAll = () => {},
     onUnstageAll = () => {},
@@ -125,6 +127,21 @@
     onUnstage(targets);
   }
 
+  // Discard mirrors the stage/unstage target selection: if the clicked row is
+  // part of the current multi-selection, the whole selection (filtered to the
+  // relevant lane) is discarded; otherwise just that one file.
+  function discardStagedFromFile(file: GitFileStatus) {
+    const targets = selectedUnstageTargets(file);
+    if (targets.length === 0) return;
+    onDiscard(targets, true);
+  }
+
+  function discardUnstagedFromFile(file: GitFileStatus) {
+    const targets = selectedStageTargets(file);
+    if (targets.length === 0) return;
+    onDiscard(targets, false);
+  }
+
   let hasUnstaged = $derived(changedFiles.some((f) => f.unstaged !== null));
   let hasStaged = $derived(changedFiles.some((f) => f.staged !== null));
   let selectedCount = $derived(changedFiles.filter((f) => selectedStatusPaths.has(fileKey(f))).length);
@@ -173,6 +190,16 @@
         <Undo2 size={14} aria-hidden="true" />
         Unstage all
       </button>
+      <button
+        class="btn-sm danger"
+        type="button"
+        onclick={() => onDiscardMany(changedFiles)}
+        disabled={isBusy || changedFiles.length === 0}
+        title="Discard all changes"
+      >
+        <RotateCcw size={14} aria-hidden="true" />
+        Discard all
+      </button>
       {#if selectedCount > 1}
         <span class="status-selection-count">{selectedCount} selected</span>
         <button
@@ -195,6 +222,16 @@
           <Undo2 size={14} aria-hidden="true" />
           Unstage selected
         </button>
+        <button
+          class="btn-sm danger"
+          type="button"
+          onclick={() => onDiscardMany(selectedFiles())}
+          disabled={isBusy || selectedCount === 0}
+          title="Discard changes in selected files"
+        >
+          <RotateCcw size={14} aria-hidden="true" />
+          Discard selected
+        </button>
       {/if}
     </div>
   {/if}
@@ -241,9 +278,9 @@
                     <FileDiff size={14} aria-hidden="true" />
                     Details
                   </button>
-                  <button class="btn-sm" type="button" onclick={() => onDiscard(file, true)} disabled={isBusy} title="Discard staged changes">
+                  <button class="btn-sm" type="button" onclick={() => discardStagedFromFile(file)} disabled={isBusy || unstageTargets.length === 0} title={unstageTargets.length > 1 ? `Discard staged changes in ${unstageTargets.length} selected files` : "Discard staged changes"}>
                     <RotateCcw size={14} aria-hidden="true" />
-                    Discard
+                    {unstageTargets.length > 1 ? `Discard ${unstageTargets.length}` : "Discard"}
                   </button>
                 {:else}
                   <span class="quiet">No staged change</span>
@@ -267,9 +304,9 @@
                     <FileDiff size={14} aria-hidden="true" />
                     Details
                   </button>
-                  <button class="btn-sm" type="button" onclick={() => onDiscard(file, false)} disabled={isBusy} title="Discard unstaged changes">
+                  <button class="btn-sm" type="button" onclick={() => discardUnstagedFromFile(file)} disabled={isBusy || stageTargets.length === 0} title={stageTargets.length > 1 ? `Discard unstaged changes in ${stageTargets.length} selected files` : "Discard unstaged changes"}>
                     <RotateCcw size={14} aria-hidden="true" />
-                    Discard
+                    {stageTargets.length > 1 ? `Discard ${stageTargets.length}` : "Discard"}
                   </button>
                 {:else}
                   <span class="quiet">No unstaged change</span>